1. Field of the Invention
The present invention relates to a method for producing a polybutadiene material. More particularly, the present invention relates to a method for producing a polybutadiene material including a 1,2-polymerization step of 1,3-butadiene in the presence of a new type of 1,2-polymerization catalyst.
2. Description of the Prior Art
It is known that a syndiotactic 1,2-polybutadiene having a high melting point can be obtained by the polymerization of 1,3-butadiene in a polymerization solvent in the presence of a 1,2-polymerization catalyst consisting of a cobalt compound soluble in the polymerization solvent, a trialkyl aluminum, and carbon disulfide and/or phenyl isothiocyanate.
It is also known that a cis-1,4-polybutadiene can be produced by the polymerization of 1,3-butadiene in a polymerization solvent in the presence of a cis-1,4-polymerization catalyst consisting of a cobalt compound soluble in the polymerization solvent and an organic aluminum halide.
In Japanese Unexamined Patent Publication (Kokai) No. 56-88,410 (1981), it was disclosed for the first time that 1,2-polybutadiene can be produced by using an organic aluminum halide as a catalytic component of the 1,2-polymerization catalyst. That is, the Japanese publication (Kokai) discloses a process for producing 1,2-polybutadiene by polymerizing 1,3-butadiene in a polymerization solvent in the presence of a catalyst consisting of a cobalt compound soluble in the polymerization solvent, a dialkyl aluminum halide, carbon disulfide, and an electron donor organic compound.
However, a comparison of this type of polymerization process, wherein a cobalt compound-dialkyl aluminum halide-carbon disulfide-electron donor type catalyst is used, with the above-mentioned type of polymerization process, wherein a cobalt compound-trialkyl aluminum-carbon disulfide type catalyst is used, shows that the former process is more disadvantageous than the latter process in that the polymerization activity of the catalyst which corresponds to the yield of polybutadiene per unit time of polymerization and per unit amount of the cobalt compound is poor and/or the resultant 1,2-polybutadiene exhibits an unsatisfactorily low intrinsic viscosity [.eta.], determined in tetrahydronaphthalene at a temperature of 135.degree. C., and, therefore, an unsatisfactorily small molecular weight.
Japanese Examined Patent Publication (Kokoku) No. 49-17666 discloses a process for producing a polybutadiene rubber having enhanced mechanical strength. In this process, a solution of 1,3-butadiene dissolved in an inert organic polymerization solvent is subjected to a cis-1,4-polymerization step in the presence of a cis-1,4-polymerization catalyst consisting of a cobalt compound and a halogenated organic aluminum compound of the formula AlR.sub.n X.sub.3-n, wherein R represents an alkyl radical having from 1 to 6 carbon atoms, a phenyl radical, or a cycloalkyl radical; X represents a halogen atom; and n represents the number of from 1.5 to 2, to convert at least a portion of 1,3-butadiene to cis-1,4-polybutadiene. Next, the resultant polymerization mixture, to which may or may not be added an additional amount of 1,3-butadiene and/or the inert organic solvent, is subjected to a 1,2-polymerization step in the presence of a 1,2-polymerization catalyst consisting of a cobalt compound, an organic aluminum compound of the formula AlR.sub.3, wherein R is as defined above, and carbon disulfide to convert the remaining portion of 1,3-butadiene to 1,2-polybutadiene. In this type of process, the 1,2-polymerization catalyst contains the organic aluminum compound of the formula AlR.sub.3 as a catalytic component.